Crowds
Look for crowds! An empty restaurant is usually a bad restaurant. There are some trendy retaurants that are always full but have bad food, but you'll be able to tell which ones those are.

Manners
Don't be afraid to send food back to the kitchen if it's not to your liking. Never let manners get in the way of a good meal. It should never be a problem to satisfy a customers needs.

Reservations
Good restaurants tend to become crowded around 7pm, so make reservations (if possible) or plan to wait for a table. Remember -- there's a reason certain restaurants are crowded. You should be able to tell if the wait is worth it!

Tipping
A quick method for calculating the tip is to double the tax. I usually do 10% for average service, or 20% for good service. I don't mind giving even more for great service. I believe you should take care of the people who are taking care of you. It is their job to bring you food, but they don't have to be kind and helpful. Take care of your server.